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Re: re: Patch plans reply

Russ you probably have a good idea here in that the "experts" in the
field have designed this feed as well as make provision for accurately
making sure that polarization is truly circular, but it is SO complex!
     Why not start with something far simpler?  Most offset fed dishes
have an F/D of abound .5 to .6 so the patch is ideal.  Take a gook at
these URL's and see if a simpler approach might be a better first step:

this is shrouded feed which I prefer to reduce side lobes.....and

These are full construction drawings which you wanted and are set up
for left-hand polarization to feed a dish.  To have the ability to work
from success seemed far better than any other method in my view.
Cliff K7RR

"Renaud, Russ" wrote:
> Cliff;
> OK, so a round patch has to have two feed points for circular polarization.
> I think I can live with that limitation, if the method of feeding the patch isn't too difficult.
> Looking at the article at:
> http://www.amsat.org/amsat/sats/phase3d/antennas.html
> the article talks about using a 50 ohm feed point, with a 1/4 wave length
> of UT-141, connected to a 100 ohm feed point to achieve circular
> polarization.
> I think UT-141 is 50 ohms characteristic impedance.  So connecting a 50 ohm
> source, through a 1/4 wave line gives one 50 ohms at the input of the line.
> But according to the article, the 'main feed' point is 100 ohms.  Isn't 100
> ohms
> in parallel with 50 ohms the equivalent of approx 33 ohms?
> I can't see how they get 50 ohms from that setup without using some sort of
> matching circuit.  I must be mssing something.  Any ideas?
> Pictures would help <grin>
> What I would like to do is build a relatively foolproof and efficient
> feedhorn
> for 2.4 gHz that can be used with a DSS offset dish.  I'm looking a square
> diagonal
> horn with a flared section (a la N7ART) but without using the polarizers as
> shown by
> N7ART.
> Take a look at:
> http://www.nitehawk.com/rasmit/n7art_tt1.html
> I'm hoping to use a round patch instead of the crossed dipoles, and flaring the horn to narrow the beamwidth and reducing the edge currents,
as suggested by W1GHZ.
> A square or rectangular patch would be too big, as it would have to be
> rotated
> by 90 degrees to properly excite the diagonal horn, so it doesn't fit.
> What do you think?
> Thanks
> Russ in FN25fl
> -----Original Message-----
> From: cbuttsch@slonet.org [mailto:cbuttsch@slonet.org]
> Sent: May 31, 2002 11:49 AM
> To: Renaud, Russ
> Subject: Re: [amsat-bb] re: Patch plans anyone?
> Russ, that is the SAME article!  I did not know you could get it on the
> web.  Congratulations on your find.
>      If you are going to use a round patch, then you must have two feed
> points---one will not do.  If your willing to make the patch oblong or
> elliptical then one will do as the G3RUH design.  This indeed is one in
> which good test equipment is required as each is individually tuned.
>      The square patch can be fed with one feedline but in order to get
> circularity the patch must be a rectangle rather than square.  The short
> side is resonant above the design frequency and the longer side below
> by an equal amount.  The program PATCH16 can help here.
>      Are you trying for a 2.4 Gc antenna?  If so a series of 2 1/2 inch
> patches on a 4 foot square sheet of metallic reflector might work well!
> Cliff K7RR
> "Renaud, Russ" wrote:
> >
> > Thanks Cliff.
> >
> > Could you confirm if this is the same article that appears at:
> >
> > http://www.amsat.org/amsat/sats/phase3d/antennas.html
> >------------------snip---------------
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